In the context of telephone termination equipment, it is necessary to provide at the termination location a printed circuit board which has circuit components to handle the signals, to provide for certain test functions, and, generally, to provide the interface between a customer's (user's) equipment and the local telephone equipment. The circuits provided on these printed circuit boards can vary somewhat, depending on the specific use. The circuits themselves are conventional and do not form part of the present invention.
The manner in which the boards are employed depends upon the number of boards needed in a specific location. Each board normally has an edge connector along a rear edge of the board. If only one board is needed, as is often the case, the board is mounted in its own housing which contains a receptacle to receive the edge connector. The receptacle is mounted on a separate PC board, fixedly mounted at the rear of the housing, which can also have a terminal strip mounted on it. A rear wall of the housing is provided with connectors so that the fixed printed circuit board can be connected to wires leading to the telephone company equipment and user's equipment.
If the customer's needs are larger so that two or more boards are needed for a larger number of terminations, the boards are commonly mounted on a rack or mounting shelf which has a back plane printed circuit board with sockets to receive all of the boards. The wire connections to the users' equipment and also to the telephone company equipment are then made to the back plane. It should be noted that each termination generally requires its own printed circuit board. Commonly, these boards are associated with four-wire dedicated telephone lines to permit synchronous or asynchronous duplex communication.
When a customer starts out with one or two terminations and thus has one or two printed circuit boards mounted in individual housings and then later requires multiple printed circuit boards, it is presently common practice to remove the boards from their housings and plug them into the back plane sockets of a shelf or rack. The individual housings are then no longer usable. They are, however, quite expensive because they include the fixed printed circuit board, the components mounted thereon, and also the various connectors mounted on the printed circuit board as well as in the rear wall of the housing. Because of the cost of these housing assemblies, the housings are either discarded at considerable loss or, more frequently, an effort is made to test, refurbish and return each housing to inventory for future use. However, this "recycling" process is, in itself, a costly one.